net: dsa: microchip: determine number of port irq based on switch type

Currently the number of port irqs is hard coded for the lan937x switch
as 6. In order to make the generic interrupt handler for ksz switches,
number of port irq supported by the switch is added to the
ksz_chip_data. It is 4 for ksz9477, 2 for ksz9897 and 3 for ksz9567.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>